fix(bt): remove unselected files from the correct download path

internal/protocol/bt/fetcher.go

@@ -399,7 +399,11 @@ func (f *Fetcher) Wait() (err error) {
 							}
 						}
 						if !selected {
-							util.SafeRemove(filepath.Join(f.meta.Opts.Path, f.meta.Res.Name, file.Path()))
+							// Path already includes the torrent's root directory.
+							name := filepath.Join(f.meta.Opts.Path, file.Path())
+							if err := util.SafeRemove(name); err != nil {
+								return fmt.Errorf("remove unselected torrent file %q: %w", name, err)
+							}
 						}
 					}
 					return

internal/protocol/bt/selection_test.go

@@ -1,11 +1,19 @@
 package bt
 
 import (
+	"context"
+	"crypto/sha1"
+	"os"
+	"path/filepath"
 	"testing"
+	"time"
 
 	"github.com/GopeedLab/gopeed/internal/fetcher"
 	"github.com/GopeedLab/gopeed/pkg/base"
 	"github.com/anacrolix/torrent"
+	"github.com/anacrolix/torrent/bencode"
+	"github.com/anacrolix/torrent/metainfo"
+	"github.com/anacrolix/torrent/storage"
 )
 
 func TestStartUsesSelectionSubmittedAfterResolve(t *testing.T) {
@@ -52,3 +60,102 @@ func TestStartUsesSelectionSubmittedAfterResolve(t *testing.T) {
 		t.Fatal("resume selected an unselected file")
 	}
 }
+
+func TestWaitCleansUnselectedFilesFromSharedPiece(t *testing.T) {
+	for _, mode := range []string{"partial", "all", "already removed", "remove error"} {
+		t.Run(mode, func(t *testing.T) {
+			dir := t.TempDir()
+			keepPath := filepath.Join(dir, "bundle", "keep.txt")
+			skipPath := filepath.Join(dir, "bundle", "nested", "skip.txt")
+			if err := os.MkdirAll(filepath.Dir(skipPath), 0755); err != nil {
+				t.Fatal(err)
+			}
+			if err := os.WriteFile(keepPath, []byte("keep"), 0644); err != nil {
+				t.Fatal(err)
+			}
+			if err := os.WriteFile(skipPath, []byte("skip"), 0644); err != nil {
+				t.Fatal(err)
+			}
+			// Both files occupy the same piece, so downloading keep.txt also writes skip.txt.
+			hash := sha1.Sum([]byte("keepskip"))
+			info := metainfo.Info{Name: "bundle", PieceLength: 16, Pieces: hash[:], Files: []metainfo.FileInfo{
+				{Length: 4, Path: []string{"keep.txt"}},
+				{Length: 4, Path: []string{"nested", "skip.txt"}},
+			}}
+			store := storage.NewFileOpts(storage.NewFileClientOpts{
+				ClientBaseDir:   dir,
+				TorrentDirMaker: func(baseDir string, _ *metainfo.Info, _ metainfo.Hash) string { return baseDir },
+			})
+			defer store.Close()
+			config := torrent.TestingConfig(t)
+			config.DisableTCP = true
+			config.DisableUTP = true
+			c, err := torrent.NewClient(config)
+			if err != nil {
+				t.Fatal(err)
+			}
+			defer c.Close()
+			spec, err := torrent.TorrentSpecFromMetaInfoErr(&metainfo.MetaInfo{InfoBytes: bencode.MustMarshal(info)})
+			if err != nil {
+				t.Fatal(err)
+			}
+			spec.Storage = store
+			tor, _, err := c.AddTorrentSpec(spec)
+			if err != nil {
+				t.Fatal(err)
+			}
+			ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+			defer cancel()
+			if err := tor.VerifyDataContext(ctx); err != nil {
+				t.Fatal(err)
+			}
+			f := &Fetcher{torrent: tor, meta: &fetcher.FetcherMeta{Opts: &base.Options{Path: dir, SelectFiles: []int{0}}}, data: &fetcherData{}, torrentDropCtx: ctx}
+			f.torrentReady.Store(true)
+			f.updateRes()
+			if mode == "all" {
+				f.meta.Opts.SelectFiles = []int{0, 1}
+			}
+			if !f.isDone() {
+				t.Fatal("selected file is not complete")
+			}
+			if mode == "already removed" || mode == "remove error" {
+				if err := os.Remove(skipPath); err != nil {
+					t.Fatal(err)
+				}
+			}
+			if mode == "remove error" {
+				if err := os.Mkdir(skipPath, 0755); err != nil {
+					t.Fatal(err)
+				}
+				if err := os.WriteFile(filepath.Join(skipPath, "child"), []byte("preserve"), 0644); err != nil {
+					t.Fatal(err)
+				}
+			}
+			err = f.Wait()
+			if ctx.Err() != nil {
+				t.Fatal(ctx.Err())
+			}
+			if mode == "remove error" {
+				if err == nil {
+					t.Fatal("cleanup failure was silently ignored")
+				}
+			} else if err != nil {
+				t.Fatal(err)
+			}
+			data, err := os.ReadFile(keepPath)
+			if err != nil || string(data) != "keep" {
+				t.Fatalf("selected file changed: %q, %v", data, err)
+			}
+			if mode == "all" {
+				data, err := os.ReadFile(skipPath)
+				if err != nil || string(data) != "skip" {
+					t.Fatalf("selected file changed: %q, %v", data, err)
+				}
+			} else if mode != "remove error" {
+				if _, err := os.Stat(skipPath); !os.IsNotExist(err) {
+					t.Fatalf("unselected file remains: %v", err)
+				}
+			}
+		})
+	}
+}